It is known that the formation of extruded foams in the form of billets or boards is enhanced by the employment of a vacuum chamber so that the expansion of the foam is accomplished under subatmospheric pressure. Examples of vacuum foam extrusion apparatus and methods may be seen in prior U.S. Patents to Nelson et al No. 3,584,108, Maxson No. 3,169,272, Cogliano No. 3,822,331, and U.K. Pat. No. 1,233,088. In vacuum extrusion technology, the most difficult to solve problem is the curing and extraction of the material, especially delicate or fragile materials from the vacuum chamber. This problem has been solved by the employment of an inclined barometric leg as seen in applicant's prior U.S. Pat. Nos. 3,704,083 and 4,044,084.
In a large scale plant relatively large single or tandem extruders are employed which are connected to a die within the vacuum chamber. In addition to the relatively large and heavy die, additional equipment is employed within the chamber such as shaping or forming mechanisms and conveyors. Although the process is continuous during production, access to the interior of the chamber is required periodically for cleaning, maintenance, and equipment removal and replacement.